Communication systems and switching structures or switching networks operating according to an asynchronous transfer mode are provided for future communication systems, particularly broadband networks. In this asynchronous mode packets having a fixed length, referred to as cells in the technical field, are transmitted in an uninterrupted fashion on every transmission section. These cells are composed of 48 octets for the useful information and of 5 octets for the cell header. When there is no useful information to be transmitted, specifically marked idle signals are transmitted.
A communication system or switching network operating according to the asynchronous transfer mode is structured into one or more network or switching stages, similar to a communication network or to the switching network of traditional digital communication networks or communication systems. The individual communication systems or switching stages are meshed with one another such that a largely blocking-free communication system or a switching structure results. The input and output lines of such a communication system or switching structure are identified from the switching-oriented information recited in the cell header of the cell, i.e. from virtual path information and virtual channel information. This switching-oriented information is derived from the multi-addressing information and destination information signalized by the subscribers of a communication system, i.e. telephone numbers of the destination subscribers.
It is known from the publication "ATM-Technologie ruer zukuenftige Breit-bandnetze" of Siemens AG, page 17, right-hand column to additionally identify routing information for the switching of a cell through a switching structure from the switching information recited in the cell header of the cell and to attach this to the cell. Using this routing information, the respective cell seeks the defined path through an n-stage switching structure under self-control, i.e. without the cooperation of a central communication system controller. The additional routing information is inserted into an internal cell header of the communication system and is placed in front of the respective cell. After the self-switching of the cell through the switching structure, the internal cell header of the communication system is removed.
The data scope of the switching-oriented information of the cell header or of the internal cell header of the communication system is essentially defined by the plurality of communication systems or of switching stages. One information string, for example, one byte, is usually provided for a communication system or a switching stage, these being compiled to form a block. Cell headers or internal cell headers of the communication system are being defined to an increasing degree that have a prescribed plurality of information strings matched to the maximum plurality of communication systems or switching stages, for example 5 bit octets or bytes for 5 communication systems or switching stages.
In the case of multi-address transmission of cells to a plurality of output lines of the communication network or of the switching structure, the self-control principle of the cells can no longer be maintained without further measures given cell headers or internal cell headers of the communication system that are structured in this way.
Consequently, routing information additionally calculated by a central communication system controller are stored in table form in the memories allocated to the communication systems or switching stages. The respective cell is communicated again via one or more branching paths to the prescribed output lines using this additionally calculated routing information.